Statistical Significance

p ,14,15 p ,22,24,26

 The medical director of a company institutes a health promotion campaign to encourage employees to exercise more and eat a healthier diet. One measure of the effectiveness of this program is a drop in blood pressure. The director chooses a random sample of 50 employees and compares their blood pressures from physical exams given before the campaign and a year latter. The mean change in systolic blood pressure for these n=50 employees is x- bar = -6. We take the population standard deviation to be σ= 20. The director decides to use a significance level of α =.05

 Population:  Parameter of Interest:  Hypothesis:  Conditions:  Calculations and Picture:  P-value:  Conclusion:

 Bottles of a popular soda are supposed to contain 300 milliliters of soda. There is some variation from bottle to bottle because the filling machinery is not perfectly precise (though it is unbiased.) The distribution of the contents is Normal with σ = 3ml. An inspector who suspects that the bottler is under filling measure the contents of six randomly selected bottles from a single day’s production. The results are:  299.4, 297.7, 301.0, 298.9, 300.2, 297.0

 Population:  Parameter of interest:  Hypothesis:  Conditions:  Calculations and picture:  P-value  Conclusions:

Statistically Significant does not mean important.

 If a significance test is significant at α =.01, must it also be significant at α =.05?  Comment on the p-value and draw a picture.

 If a significance test is significant at α =.05, must it also be significant at α =.01?

 You are performing a significance test of H o : µ= 0 based on an SRS of 20 observations from a Normal population.  A. If Ha: µ > 0, what values of the z-statistic are significant at the α =.005 level?  B. If Ha: µ <> 0, what values of the z-statistic are significant at the α =.005 level? 

 Asked to explain the meaning of “statically significant at the α =.05 level,” a student says: “This means that the probability that the null hypothesis is true is less than.05.  What is wrong with this statement?  Give the correct interpretation.